At present routine methods for preparing fuel-air mixture for internal combustion engines consists in producing a hydrogen-containing gas from liquid fuel and adding said gas to the fuel-air mixture.
However, the liquid fuel decomposing reaction according to the heretofore-known methods occurs in the presence of highly expensive platinum-based catalysts at rather high temperatures (cf. U.S. Pat. No. 4,147,142). The catalysts need regular replacement in the course of operation. Presence of antiknocking additives are detrimental to catalysts. And use of only the heat of exhaust gases for fuel decomposition is inadequate to attain an efficient and stable running of the fuel decomposition process.
Therefore higher temperature of the fuel-air mixture is attained by burning part of the fuel, thus increasing its consumption (cf. U.S. Pat. No. 3,901,197). Then the thus-preheated mixture is fed to the catalytic chamber and whence to the internal combustion engine. However, use of an open fire is hazardous under conditions of an internal combustion engine. A danger of flame travel and an outbreak of fire arises when engine runs unsteadily or misses, as the velocity of flame travel in the fuel-air mixture may exceed the flow velocity of the mixture itself.
Moreover, unburnt hydrocarbons of the CnHn+2 type are left after burning an enriched mixture, which are deposited in the catalyst pores as soot and coke, thus putting the catalyst out of order. On the other hand, the use of only the heat of ICE exhaust gases for fuel decomposition is inadequate to attain an efficient and stable running of the fuel decomposition process.
Therefore a higher temperature of the mixture is attained by burning part of the fuel, thus adding to its consumption (U.S. Pat. No. 3,901,197). Then the thus preheated mixture is fed first to the catalytic chamber, then to the engine.
However, use of an open fire in an internal combustion engine is hazardous. A danger of flame travel and an outbreak of fire arises when an engine runs unsteadily or misses, as the velocity of flame travel in the fuel-air mixture may exceed the flow velocity of the mixture itself.
As an enriched mixture cannot be burnt completely, it comprises unburnt hydrocarbons of the CnHn+2 type which are deposited in the catalyst pores as soot and coke, thus putting the catalyst out of order.
DE Pat. A1 #3,607,007 provides for heating one of the mixture flows on a hot blind end of a special piping, which is of low efficiency due to a steam-and-gas cushion forming on said end face, as well as a considerable aerodynamic drag offered to the running flow of mixture. Furthermore, the fuel decomposition reaction runs as an endothermic one and at a high temperature which is not provided by the method in question, whereas use of exhaust gases having a temperature of 750.degree. C. in the area of the valve seat is impossible as said temperature drops abruptly in the direction away from said are towards the end face of the piping being heated.
One prior-art device for preparing fuel-air mixture is known to comprise an additional heating arrangement with an ignition spark and a burner to which the fuel-air mixture is fed and burns therein in an open fire, after which said mixture is fed to the reactor with a catalyst, wherein part of the liquid fuel molecules get decomposed (DE B2 2,613,348).
However, the use of an open fire and of expensive and short-lived catalysts, as well as diseconomy of said methods and devices render their application in the engine-building industry inefficient.
As regards heat-exchangers used particularly in the engine-building industry, they should meet the requirements as to minimizing aerodynamic drag or loss of head of running flows. Such requirements is of special importance for devices for heat-exchanging between low-pressure or vacuumized gas flows.
Known in the art are devices for heat exchange between exhaust gases of an internal combustion engine and fuel-air mixture, as well as devices for liquid-gas fuel conversion directly on a vehicle (FRG Pat. #3,607,007, USSR Inventor's Certificate #493,073, Russian Federation Pat. #2,008,495).
Liquid-fuel converting systems operate in internal combustion engines concurrently with the existing routine fuel-air preparing systems featuring low aerodynamic drag. Hence when said drag in the conversion system increases considerably, efficiency of the system is very low.
Closest to the method proposed herein is the one known from Pat. #2,008,494 of the Russian Federation, consisting in that two flows of fuel-air mixture are established and get overrich, one of which is heated with exhaust gases and then further heated by being passed through a promoter preheated to a temperature above the mixture ignition point, whereupon fuel thermal cracking is effected in the boundary layer of said activator by many-times repeated bringing said layer in contact with the activator surface.
The closest to the proposed device is the one according to Pat. #2,008,495 of the Russian Federation, comprising a double-loop heat-exchanger having an inlet and an outlet piping, a first loop of the heat-exchanger being a gas one, and a second loop of said heat-exchanger comprises a mixer-proportioner of the components of the mixture being handled and a mixing connector, an incandescent element provided at the heat-exchanger outlet, and an exhaust pipe of the engine, while the inlet and outlet pipes of the heat-exchanger gas loop are connected to the engine exhaust pipe and to the atmosphere, respectively, the proportioner mixing pipe communicates, via a control member, with the heat-exchanger mixing loop, while the incandescent member is of the nonigniting type and appears as a promoter having a well-developed heatable surface and located in the outlet pipe of the heat-exchanger mixture loop.
Closest to the heat-exchanger proposed herein is the one as per FRG Application #2,408,462, IPC F 28 D 9/00, wherein used as a heat-exchanging element is a corrugated plate isolating the flows of the matter being handled from one another. The corrugations define alternating cells or flow passages for the heat transfer agent and the substance being preheated to run therealong.
However, said flows of the matter are fed and withdrawn by being twice turned through 90 degrees both at the heat-exchanger inlet and outlet, thus adding much to the aerodynamic drag and increasing local head loss Hll:
H.sub.ll =E.V.sub.2 /2g,
where E is the drag coefficient (1.129) at the flow turn through 90 deg.;
V is the flow velocity; and PA1 g is gravitational acceleration.
With the four times repeated turn of one flow, E=1.625.
To overcome said aerodynamic drag requires an additional amount of energy which involves, under conditions of a vehicle, higher fuel consumption and affects adversely the efficiency of the fuel conversion system. Such a construction arrangement of input/output devices renders the heat-exchanger bulky, whereby it cannot always be arranged on a vehicle.
Use of construction members adding to the heat-exchange surface area in heat-exchangers for fuel conversion systems is also restricted as increasing the aerodynamic drag. As a rule, heat-exchangers of such systems operates at a low rarefaction (or pressure) thereinside (0.2-0.8 kPa) which in turn imposes its own construction requirements on the heat-exchanger components. Thus, for instance, the shell and corrugations of a heat-exchanger may be made of metal sheets 0.2-0.3 mm thick which simplifies production techniques, improves heat-transfer conditions, and reduces thermal lag of the heat-exchanger.